1. Technical Field of the Invention
The present invention relates in general to the field of communications, and in particular, by way of example but not limitation, to tuning to signal path-rays in a wireless communications system such as a Code Division Multiple Access (CDMA) system.
2. Description of Related Art
Mobile wireless communication is becoming increasingly important for providing safety, convenience, improved productivity, and simple conversational pleasure to subscribers of wireless communications services. One prominent mobile wireless communication option is cellular communication. Cellular phones, for instance, can be found in cars, briefcases, purses, and even pockets. With the proliferation of cellular phone users and the types of services offered, new wireless system standards are being developed to meet these demands.
For example, CDMA, Wideband-CDMA (W-CDMA), etc. are being implemented to improve spectral efficiency and introduce new features. In CDMA or W-CDMA (jointly referred to as “CDMA” hereafter), signal fading is combated by combining multiple received diverse signal path-rays in a RAKE receiver. Locations (in time) of the signal path-rays are first found by using a searcher. Subsequently, these path-rays are combined by using a maximum ratio combiner (MRC). Searchers are conventionally implemented as one or more matched filters and a peak detector. The signal path-rays are matched to a certain pilot sequence, which results in peaks that indicate the locations of the various path-rays. The peak detector detects these resulting peaks.
Realizing a searcher is a computationally complex endeavor; therefore, it is desirable to detect the path-rays only once. After detection, the path-rays are consequently tracked as long as possible by using a path-ray tracker. The tracking is continued until the quality of the received signal reaches (e.g., falls) to a predetermined threshold. Thereafter, the tracking is ceased and a new search is initiated. The computational complexity of a searcher results from, at least in part, the number of delay candidates that the searcher must consider in order to locate the path-rays. The greater the number of delay candidates, the greater the cost in terms of hardware, processing time, power consumption, silicon real estate, etc. Hence, there is a need for a means to reduce the total number of delay candidates that must be considered by the searcher when locating the diverse signal path-rays.